The specificity of tumour therapy often constitutes a limiting factor in determining the success of the treatment. In fact, the onset of toxic effects and the reduced tolerability of a number of anticancer agents limit their use and the quality of life of the patients.
The reduction of toxicity is directly linked to the selectivity of the treatment for cancer cells alone. Monoclonal antibodies are the ideal instrument for specifically localising the tumour and, when combined with the avidin/biotin amplification system, constitute an extremely potent method for directing active molecules to the tumour site.
Tenascin is a molecule of the extracellular matrix, expressed during embryogenesis and in adult tissues during the processes of scar formation and tumour development, as well as in newly formed blood vessels. Tenascin is virtually absent in normal adult tissues, whereas it is expressed in the stroma of many solid tumours such as gliomas (Burdon, et al., Cancer. Res., 43:2796-2805, 1983), carcinomas of the breast (Chiquet-Ehrismann, et al., 1986), lung (Natali, et al., Intl. J. Cancer, 54: 56-68, 1989), fibrosarcomas and squamous-cell carcinomas (Ramos, D. M. et al., Intl. J. Cancer, 75:680-687, 1998). Tenascin is expressed in glioma, but not in the corresponding normal brain tissue. For an in-depth discussion of tenascin, the reader is referred to WO 92/04464, Wistar and related references.
On the basis of EP 0 496 074, G. Paganelli et al. have developed a method called “three-step pre-targeting” for the systemic and locoregional treatment of tumours, the results of which are reported in: Cremonesi, M., et al., Eur. J. Nucl. Med., 26 (2):110-120, 1999; Paganelli, G., et al., Eur. J. Nucl. Med., 26 (4):348-357, 1999; Paganelli, G., et al., Cancer Biother. & Radiopharin., 16 (3):227-235, 2001; Grana, C., et al., Br. J. Cancer, 86:207-212, 2001.
Other references for this type of cancer treatment are: WO 94/04702, and U.S. Pat. No. 5,578,287.
Three-step pre-targeting treatment, also known sotto by the trade-mark PAGRIT®, is based on the sequential intravenous administration of a biotinylated anti-tenascin monoclonal antibody, streptavidin and 90Y-biotin, with administrations of avidin and biotinylated albumin prior to the streptavidin and 90Y-biotin, respectively (“chase” step), to reduce the circulating levels of the antibody and of streptavidin. The selectivity of the 3-step pre-targeting method is due to the use of the anti-tenascin monoclonal antibody. The targeting of extracellular matrix molecules presents the advantage, compared to targeting aimed at cell surface antigens, of not being affected by modulation of antigen expression by the tumour cell itself. The doses, administration times and “chases” of the pre-targeting treatment have been established for the purposes of obtaining optimal tumour to non-tumour biodistribution ratios.
The results obtained in 48 patients suffering from glioblastoma (GBM) or anaplastic astrocytoma (AA), entered into a study by Paganelli (Paganelli, G., et al., Eur. J. Nucl. Med., 26 (4):348-357, 1999), have demonstrated a substantial lack of toxicity, except for a number of cases of allergic reaction to streptavidin, and preliminary efficacy of the treatment. In fact, 2 months after the end of the treatment, 25% of the patients showed a reduction of the tumour mass (Complete Response=6%, Partial Response=11%, Minor Response=8%), and 52% of patients remained stable, with an overall response rate of 77%. In a number of these patients, whose life expectancies were below six months, the response to treatment persisted for more than one year.
The role of the biotinylated anti-tenascin antibody is to localise in the tumour and mediate, via the biotinylated molecule, the accumulation of avidin and subsequently of 90Y-biotin, directing the radioisotopes directly into the interior of the tumour. Anti-tenascin antibodies are already the object of patents and patent applications: U.S. Pat. No. 5,624,659, Duke University; JP 2219590, Rikagaku; WO 92/04464, Wistar; and WO 03/072608, Sigma-Tau.
One particular anti-tenascin antibody is described in: Siri, A., et al, Nucl. Acid Res., 19(3):525-531, 1991; Balza, E., et al, FEBS 332:39-43, 1993; and its use for therapeutic purposes is described in: Riva, P., et al., Acta Oncol. 38(3):351-9, 1999; Riva, P., et al, Cancer, 80 (12): 2733-42; 1997; Riva, P., et al., Int. J. Cancer, 5:7-13, 1992.
The clone used for the generation of said antibody in the above-cited studies is called BC-2. The applicant has demonstrated that the clone BC-2 is not suitable for industrial development, in that it produces an additional non-functional light chain (probably deriving from the parent myeloma line) whose level of expression increases during development of the production process on a large scale, preventing industrial-scale purification of the antibody.
There is therefore a perceived need for an anti-tenascin monoclonal antibody that can be produced on an industrial scale at the purity levels required for pharmaceutical use.
The previous patent application WO 03/072608, filed in the name of Sigma Tau Industrie Farmaceutiche Riunite S.p.A., describes the generation of the anti-tenascin antibody ST2146, without the additional non-functional light chain, capable of recognising an antigenic epitope shared with antibody BC-4, also contaminated by a non-functional light chain.
Antibody ST2485, the object of the present invention, recognises an epitope partly shared with that of BC-2, and therefore located in the same protein region. This region is greatly expressed in various tumour tissues. It is therefore important to have a homogeneous monoclonal antibody which is specific for this region, to be used for cancer diagnosis or targeting.
Moreover, the present invention demonstrates that antibody ST2485 presents the advantage of binding to tenascin in addition to antibody ST2146, thus proving useful in pre-targeting methods involving the combined use of the two antibodies.